The purpose of this project is to investigate the changes in semantic memory that occur in normal aging and dementia. Semantic memory will be assessed with a set of well-researched laboratory tasks, while brain activation will be measured using positron-emission tomography (PET). PET activation studies will be conducted in 10 young normal and 10 old normal control subjects and 10 probable AD patients performing Visual Confrontation naming, Visual Semantic Process and Word Reading. It is hypothesized that the activity in low-level automatic processing systems will be normal in Alzheimer's disease (AD) whereas the processes requiring flexibility and active search will result in compensatory hyperactivation in the AD patients.